docs: def present_participle(self, word):
          """
          Return the present participle for word.
  
          word is the 3rd person singular verb.
  
          """
          plv = self.plural_verb(word, 2)
  
          for pat, repl in (
              (r"ie$", r"y"),
              (r"ue$", r"u"),  # TODO: isn't ue$ -> u encompassed in the following rule?
              (r"([auy])e$", r"\g<1>"),
              (r"ski$", r"ski"),
              (r"[^b]i$", r""),
              (r"^(are|were)$", r"be"),
              (r"^(had)$", r"hav"),
              (r"^(hoe)$", r"\g<1>"),
              (r"([^e])e$", r"\g<1>"),
              (r"er$", r"er"),
              (r"([^aeiou][aeiouy]([bdgmnprst]))$", r"\g<1>\g<2>"),
          ):
              (ans, num) = re.subn(pat, repl, plv)
              if num:
                  return "%sing" % ans
          return "%sing" % ans